1. Field of the Invention
The present invention relates to a sealed battery and a method for manufacturing the same, and more particularly to an electrode post structure which enables reductions to be achieved in the weight of the battery, the number of components, and the battery cost, while retaining highly reliable sealing of the electrolyte.
2. Description of the Related Art
In recent years, environmental concerns have prompted considerable interest in electric vehicles and hybrid vehicles that use fuel cells or rechargeable batteries as a power source, and the rechargeable battery that functions as the power source or auxiliary power source for these vehicles should ideally be as small and as light as possible, while providing maximum capacity and output. Examples of sealed rechargeable batteries that satisfy these requirements include lithium ion rechargeable batteries and nickel-metal hydride batteries.
In these types of sealed batteries, if a metal case is used to reduce gas permeation and improve the cooling properties of the battery, then the electrode post that functions as the external connection terminal must be insulated with respect to the case and sealed with respect to the electrolyte in the region where the post passes through the case.
One example of a conventional electrode post construction is shown in FIG. 8 (see Japanese Patent Laid-Open Publication No. Hei 8-77999). This electrode post 41 is equipped with column sections 43, 44 at the top and bottom of a main body 42, and the lower column section 44 is inserted into an electrode post through-hole 46 formed in the case 45, with insulating packing 47 provided between the lower column section 44 and the case 45. A current collecting washer 49 that is connected to one end of an electrode plate assembly is provided on the inside surface of the case 45 with packing 48 disposed therebetween, and a crimped section 50 formed on the bottom end of the lower column section 44 connects the electrode post 41 to the current collecting washer 49 and secures the electrode post 41 to the case 45.
Another conventional electrode post construction is shown in FIG. 9 (see Japanese Patent Laid-Open Publication No. 2000-48803). This electrode post 51 is inserted into an electrode post through-hole 56 formed in the case 55, with insulating packing 52 provided between the electrode post 51 and the case 55. Additional packing 54 is provided between the inside surface of the case 55 and a packing support collar 53, which protrudes outward from the outer periphery near the bottom of the electrode post 51, and a nut 57 that is screwed onto the externally protruding section of the electrode post 51 is used to secure the electrode post 51 to the case 55.
However, in a battery pack used as the power source for a vehicle, even a reduction in weight of several hundred grams is important. Moreover, a battery pack comprises a plurality of cells connected in series to achieve the prescribed output voltage, and because the electrode posts are comparatively heavy, the weight of the electrode posts has a significant effect on the overall weight of the battery pack. Furthermore, because leakage of the electrolyte can result in short circuiting caused by corrosion, the sealing of the electrolyte must be maintained with a high level of reliability over extended periods, even under severe operating conditions.
However, in the electrode post construction shown in FIG. 8, because only the bottom end of the electrode post 41 is hollow, the weight of the electrode post is considerable. Furthermore, because the gap between the main body 42 and the crimped section 50 is sealed with respect to the electrolyte simply by compressing the insulating packing 47 between the lower column section 44 and the through-hole 46, the sealing performance varies considerably, and achieving reliable electrolyte leakage prevention over an extended period is difficult.
Furthermore in the electrode post construction shown in FIG. 9, tightening the nut 57 seals the structure by causing a compression of both the insulating packing 52 between the electrode post 51 and the through-hole 56, and the packing 54 between the packing support collar 53 and the inside surface of the case 55, and thus provides a superior seal to the construction shown in FIG. 8. However, the sealing pressure generated within the insulating packing 52 is not particularly high, meaning the sealing performance cannot be increased significantly, and the increase in the number of components causes increases in both the weight and the cost of the structure.